The present invention relates to enhancing processing of cement from clinker, and more particularly to a liquid-dispensable, high solids-loaded cement additive composition comprising at least one salt and optionally an amine, glycol, and/or carbohydrate, and to processes for making the same.
Cement additives are known for enhancing the processing of cement from the grinding of clinker, gypsum, and fillers such as limestone, granulated blast furnace slag, and other pozzolans.
Cement additives comprising salts are also known. Such additives typically comprise a calcium chloride salt or sodium chloride salt, and optionally an amine and/or a carbohydrate. Such additives, usually in the form of aqueous solutions, are intended to enhance properties of cement such as strength and set time. The maximum amount of active solids in these aqueous solutions is limited by the solubility of the least water-soluble component, which is usually the chloride salt, in the water component. Salt-containing additives, which are commercially available from Grace Construction Products, Cambridge, Massachusetts, under the tradename TDA(copyright), typically have total solids contents of 30-40% dry weight solids.
If the concentration of a given salt exceeds its solubility limit, then the salt will precipitate out of the aqueous solution and render the cement additive product difficult to use and dispense in the cement grinding operation. This is because the precipitation will clog the dispensing system and form solid masses in storage tanks. The cement additive then becomes a mixed-phase material, because one or more of its components, due to precipitation, will no longer be in solution while other components may remain in solution. The result is that the proportions of the components within the cement additive product will likely be less than ideal for the intended application, since the precipitated components will not be pumped or dispensed into the cement clinker grinding operation as intended.
Thus, one of the problems with using high concentration salt solutions is the risk that precipitation can occur. Any number of factors, such as a decrease in temperature, evaporation of water, or nucleating events such as contamination, can prompt a highly salt-saturated solution to precipitate. The precipitation will cause pump-dispensing problems and/or dosage miscalculations and inefficiencies. The typical dosage for these liquid products is 1500-2500 grams of cement additive product per ton of cement, clinker, and fillers. Hence, if the cement manufacturing plant (mill) were to use a cement additive product to produce 70 tons of cement per hour, then approximately one truckload (about 45,000 pounds) of the liquid cement additive product would be required on a weekly basis. Given the influence of the cement additive on the strength or set time performance characteristics of the cement, a missed shipment could mean that there will be a significant decrease in the quality of the cement being produced.
The shipment, storage, and handling of large volumes of liquid additive materials is highly inconvenient. However, the use of dry powders is not a more convenient or desirable alternative, because dry powders are difficult to dispense accurately -and they present a health concern due to the dust arising from the dry powder.
Accordingly, the present inventors believe that the use of a highly concentrated liquid additive provides great value and resolves problems discussed above. Until the present invention, however, it has not been possible to use and dose an extremely highly concentrated liquid salt-containing cement additive. Such a highly concentrated salt liquid, moreover, needs to be stable in suspension for long periods of time, resistant to temperature changes, and capable of being pumped so that it can be dispensed into the clinker cement grinding operation.
In surmounting the disadvantages of the prior art, the present invention provides a novel high-solids liquid cement additive compositions and method for making them. Exemplary liquid cement additive compositions of the invention comprise at least one salt, a liquid carrier, and a viscosity-modifying agent (VMA) that increases the amount of total active solids that can be suspended in the liquid carrier. If the liquid carrier is water, then exemplary embodiments of the invention further comprise a VMA-dispersing agent that not only disperses the VMA within the aqueous environment, but enhances the capacity of the liquid cement additive composition to load the salt and other cement additives at levels higher than would be possible by mere solubilization of the salt and other additives.
In particular, aqueous liquid carriers are used to dissolve a first portion of a particular cement additive (e.g., salt) while a second portion of the cement additive is suspended in the form of non-dissolved solid particles, through the use of the VMA and VMA-dispersant.
Thus, an exemplary liquid cement additive composition of the invention comprises: a liquid carrier for suspending a first cement additive, such as an alkali or alkaline earth metal salt, in the form of solid particles substantially uniformly throughout the liquid carrier. The salt may comprise a chloride, nitrate, nitrite, thiocyanate, borate, polyphosphonate, gluconate, or mixture thereof. Preferably, a second cement additive, which is different from the first cement additive, is contained within the liquid carrier as a solute and/or as non-dissolved solid particles. For example, the second cement additive may comprise an amine, an alkanolamine, a poly(hydroxyalkylated) polyethyleneamine, a glycol, a carbohydrate, a surfactant, or mixture thereof.
Exemplary liquid cement additive compositions have a total salt content of 50-90% by wt. based on total weight of said liquid cement additive composition, and a total solids content of 70%-100% by wt. based on total weight of said composition.
If the liquid carrier is an aqueous suspension, then it will be possible that a first portion of the alkali or alkaline earth metal salt is contained as a solute, while a second portion is in the form of non-dissolved solid particles, such that the liquid cement additive composition can contain solids in amounts that exceed the water-solubility factor for individual solids.
In preferred embodiments, a viscosity modifying agent (VMA), preferably with a dispersing agent operative to enhance the ability of the liquid carrier to suspend the solids (e.g., salt) particles, is used. In a preferred exemplary method, a VMA, such as biopolymer S-657, is mixed first with a polycarboxylate polymer, which is preferably a comb polymer having pendant oxyalkylene groups, and water, thereby forming a first suspension; and this first suspension is mixed with at least one alkali or alkaline earth metal salt to obtain a second suspension, which then may be used as a liquid cement additive composition which can be dispensed into the grinding operation whereby clinker is ground to provide cement.
As an alternative to the foregoing method wherein an aqueous suspension is employed, other exemplary methods of the invention involve a non-aqueous liquid carrier for dispersing the VMA. For example, a nonaqueous liquid carrier medium can include an amine, an alkanolamine, a poly(hydroxyalkylated) polyethyleneamine, a glycol, a surfactant, or mixture thereof is combined with the VMA to provide a first (nonaqueous) suspension; and then this first suspension is mixed with water to allow the VMA to hydrolyze and increase in viscosity prior to adding the at least one alkali or alkaline earth metal salt to obtain a second (aqueous) suspension. Exemplary compositions of the invention made by this method therefore comprise the nonaqueous liquid carrier, a VMA, and at least one alkali or alkaline earth metal salt, wherein the VMA and salt are present in the amount ranges summarized above.
As a further alternative, the VMA can first be dispersed in a dry blend with an alkali or alkaline earth metal salt, which is then added to a premixed combination of water and an amine, an alkanolamine, a poly(hydroxalkylated) polyethyleneamine, a glycol, a carbohydrate, a surfactant, or a mixture thereof. As the VMA hydrolyzes with mixing, the suspension will build sufficient viscosity to keep the undissolved salts in suspension.
All of the previous methods describe a system wherein the VMA is dispersed within a liquid carrier (typically of greater volume, e.g., three times) to protect the VMA from clumping when the VMA finally comes into contact with a solvent (water in the foregoing cases). This allows for most dosage-efficient use of the VMA, which is an expensive component of the final dispersion. In a further alternative method, the VMA can be effectively dispersed in water directly by using a high sheer mixer while adding the VMA to water, thus minimizing or avoiding clumping. The high sheer mixer is preferably of the continuous type, such that water and VMA are metered into a mixing chamber where a mixing element or rotor is spinning between 1000-5000 rpm, whereby the VMA is dispersed into the water. Once the VMA and water is high-shear-mixed to provide a high viscosity first suspension, then the at least one alkali or alkaline earth metal salt can be combined, using conventional mixers at slower speeds, to obtain a second (aqueous) suspension.
Thus, exemplary compositions and methods of the invention allow one or more salts to be loaded into an aqueous suspension well beyond their solubility limit, while at the same time allowing the resultant liquid cement additive-composition to be pumped as a liquid and to maintain stability across a wide range of temperatures during storage and shipment.
Due to the ability of the invention to provide high-solids additives loading, exemplary liquid cement additive compositions of the invention afford additional advantages in terms of decreased freight costs and lower frequency of deliveries. A further benefit is its ability to incorporate a wide range of components, particularly ones having low (or even no) solubility in water.
Thus, a further exemplary method of the invention for making a cement additive composition, comprises: obtaining a first liquid suspension (preferably aqueous) by combining a viscosity modifying agent, a dispersing agent operative to disperse the viscosity modifying agent (preferably in water), and a liquid carrier medium (preferably water); and obtaining a second liquid aqueous suspension by combining the first liquid aqueous suspension with at least one alkali or alkaline earth metal salt, whereby water is present in an amount of 0.1%-30% by total weight of said composition.
In preferred methods, the viscosity modifying agent (VMA) is xe2x80x9cpremixedxe2x80x9d first with the dispersing agent before the liquid carrier medium (e.g., water) is added to the first liquid aqueous suspension in order to separate and disperse the VMA and to ensure that a stable dispersion is obtained.
A preferred viscosity modifying agent (VMA) is polysaccharide S-657, which optionally may be supplemented with other VMAs (e.g., welan gum). A preferred dispersant is a polycarboxylate polymer, and more preferably a comb polymer having pendant polyoxyalkylene groups. Other exemplary dispersants include alcohols (e.g., ethanol, methanol, isopropanol), polyethylene oxide, polycarboxylic acid (which also shall be used to refer to the salt or derivatives thereof in this case), polyacrylamide; or a mixtures thereof. Amines, glycols, and combinations of these may be used as dispersing agents for S-657 in some embodiments of the invention. For some dispersing agents, such as an amine, it is preferred to use as little of the amine as possible to achieve the dispersing effect. For others, such as polycarboxylate polymer dispersants, one may need to consider keeping the amount close to the minimum level required for dispersing the VMA lest the function of any cement additives contained in the composition be diminished.
In further exemplary embodiments, at least one other cement additive can optionally be included in the cement additive composition, preferably after the first liquid aqueous suspension is obtained (i.e., after first stage) and before the alkali or alkaline earth metal salt or salts are combined to obtain the second liquid aqueous suspension. Further exemplary cement additives include a carbohydrate (e.g., sugar, sugar derivative), an amine (e.g., triethanolamine, triisopropanolamine), a glycol (e.g., ethylene glycol, diethylene glycol, propylene glycol, polyethylene glycol, etc.), a surfactant, or a mixture thereof. The amount of active solids in the second liquid aqueous suspension is preferably about 60% to 96% by total weight of composition.
The present invention thus also relates to a high solids liquid cement additive composition made by any of the foregoing methods. It also relates to cementitious compositions and methods for making such cementitious compositions whereby one of the above-described cement additive compositions is introduced to clinker or gypsum before or during the grinding operation to produce Portland cement. Preferred cement additive compositions are suspensions wherein water is present in an amount of 0.01-30% by weight of the total composition, wherein the use of the viscosity modifying agent (0.01-3.0% wt) and dispersant (0.02-4.0% wt) permit one or more alkali or alkaline earth metal salts to be present as a solute in the aqueous phase, as well as a suspended (non-dissolved) solid dispersed within the liquid medium. Additional additives, such as an amine, alkanolamine, glycol, carbohydrate, and/or surface active agent, may also contained within the liquid cement additive composition, such as by being dissolved within an aqueous phase and/or suspended in non-dissolved solid form within the liquid carrier medium (which could be water or non-aqueous) as may be applicable to the particular additive material selected.
Further features and advantages of the invention are discussed in further detail hereinafter.